The present invention relates to a thermally insulated container having a double-walled structure in which an inner container and an outer container are integrally joined leaving a space therebetween, and in particular, the present invention relates to a thermally insulated container in which a radiation prevention film is formed on at least one of the outer surface of the inner container or the inner surface of the outer container.
In recent years, thermally insulated metal containers having inner and outer containers made from metals such as stainless steel have been widely used in place of conventionally used glass vacuum flasks (hereinafter, referred to as xe2x80x9cthermally insulated containersxe2x80x9d). Because thermally insulated metal containers are superior from the point of view of strength, they are suitable for portable use.
Thermally insulated containers made from metal are made by arranging an inner container and an outer container, which are made of a metal such as stainless steel, leaving a space section in between and joining the opening sections thereof to form an integrated double walled container, and the space section is used to form a thermally insulating layer. In particular, thermally insulated metal vacuum flasks in which the space section is evacuated to form a thermally insulating vacuum layer are used generally as thermally insulated containers whose temperature maintaining performance is excellent.
However, in the above-mentioned thermally insulated metal vacuum container, since the inner and outer containers are metal, which is not transparent, it is not possible to check the quantity of the contents and the like from the outside, and in order to do this, it is necessary to remove the lid or the stopper, and check the inside of the container through the opening.
When checking the inside of the container, external air flows into the inside of the container. Therefore, when cold drink, for example, is contained in the container, the temperature of the drink increases to due to the inflow of air. In addition, when a hot drink such as hot water or the like is contained in the container, the temperature of the drink falls.
For this reason, the temperature maintaining performance of the conventional thermally insulated container was degraded.
In addition, with the above-mentioned thermally insulated glass containers, in order to prevent thermal radiation and to increase the temperature maintaining properties, it is common for a silver-plating film to be formed by means of a silver mirror reaction on the thermally insulating layer side of the inner or outer container. In this case, it is impossible to check the contents of the container from the outside. Therefore, in the same way as for the above-mentioned thermally insulated metal containers, there is a problem that maintenance of the temperature of the contents of the container is insufficient.
In addition, in Japanese Unexamined Patent Application, First Publication No. 2000-60743, a thermally insulated container in which a transparent synthetic resin is used for the inner and outer containers is disclosed.
In this thermally insulated container, a thermally insulating layer is formed in which a gas having a thermal conductivity lower than air (hereinafter, referred to as low thermal conductivity gas), such as krypton, xenon, and argon, is enclosed within the space section.
In this thermally insulated container, to prevent thermal radiation, a radiation prevention film through which visible light can pass and which absorbs or reflects infrared radiation is provided on the surface of the thermally insulating layer side of the inner or outer container.
The radiation prevention film is formed by adhering a metal oxide, a metal nitride, or fine particles of metal on a film substrate in a single layer or a multilayer by means of the vapor deposition, sputtering, ion plating, or the like.
With this thermally insulated container, since a radiation prevention film through which visible light can pass is used, it is possible to check the contents of the container from the outside through the radiation prevention film.
However, since the radiation prevention film used in this thermally insulated container has a high rigidity, it is difficult to form curved surfaces.
For this reason, it can be arranged on places such as flat sections, and sections which are broadly flat (such as the body of cylindrical sections), but arrangement on sections which are formed of curved surfaces such as the shoulders or bottoms of the container, or the like, is difficult.
In consideration of the above-mentioned circumstances, the present invention has an object of providing a thermally insulated container with which it is possible to visually inspect the contents, or the like, contained within the container, which has superior temperature maintaining performance, and which can be given an improved radiation prevention function by providing a radiation preventing performance on parts of the container which have curved surfaces as well as parts of the container which have flat surfaces.
The thermally insulated container according to a first aspect of the present invention comprises an inner container and an outer container formed of a transparent material which are arranged leaving a space section therebetween, and which are integrally joined to form a double walled container, wherein the space section between the above-mentioned inner and outer containers of the double walled container forms a thermally insulating layer, and a radiation prevention film is formed on at least one of the outer surface of the inner container and the inner surface of the outer container. The radiation prevention film has a radiation prevention film omission section having an area which is 30% or less of the container surface on which the radiation prevention film is formed.
In the thermally insulated container, the transparent material may be glass.
In the thermally insulated container, the transparent material may be synthetic resin.
In the thermally insulated container, the thermally insulating layer may be a vacuum insulation layer.
In the thermally insulated container, the thermally insulating layer may enclose a low thermal conductivity gas.
In the thermally insulated container, the radiation prevention film omission section may be formed in a slit shape in the axial direction of the container.